For Stephan J. Morris, NS, NINCDS, we have constructed a computer controlled multisignal rapid-mixing stopped-flow apparatus. This unit consists of a lamp source, wavelength monochromator, an Aminco-Morrow stopped-flow assembly, and 3 photomultipliers with their associated electronics. One photo-multiplier tube measures optical density at a particular wavelength of light and the other two photo-multipliers measures fluorescence at different wavelengths and polarizations. The electronics is designed to condition four signals, providing variable gain, offset, and switchable low pass filtering. Channel one is for optical density two and three and for the fluorescence signals, and the fourth is the lamp output signal which is used to normalize the other three channels the outputs of the four amplifiers are then input to a Dec-PDP 11/34 computer which is triggered by the stopped-flow apparatus and collects four channels of analog data at a variable rate and plots all four channels in real time. The data are then saved on disc and then is transferred to a VAX 11/780 for the analysis of the kinetics of membrane fusion of phosphalipid vesicles. Work was also done by BEIB on data analysis on the DEC 10. The programs developed are for the PDP 11/34, written in Fortran for ease of maintenance, consist of about 2,000 lines of code for the data acquistion program, and about 1,000 lines of code for a program to replot the data and print the file variable information. Future work will be to add a dual wavelength monometer and syncronization to use it.